The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention relates to encapsulated toner compositions comprised of a core comprised of a polymer resin or resins, and colorants, and a polymeric shell thereover prepared, for example, by interfacial polymerization and comprised in an embodiment of a condensation polymer derived from the reaction of glycidyl-functionalized reagents and polyisocyanates with polyamines. The aforementioned polymeric shell may also contain a soft, flexible component such as a polyether moiety primarily for the purpose of improving the packing of the shell materials. Proper packing of the shell components permits, for example, a high density shell structure, and lowers, suppresses, or in some instances eliminates the shell's permeability especially to the core resins. A high degree of shell permeability is primarily responsible for the leaching or bleeding of core binder from the toner, causing the problems of toner agglomeration or blocking, and image ghosting in imaging and printing processes, which problems are avoided or minimized with the toners of the present invention. One embodiment of the present invention relates to encapsulated toner compositions comprised of a core of polymer resin and colorants, which core is encapsulated by condensation polymers formed by interfacial polymerization between a mixture of glycidyl-functionalized reagents and polyisocyanates with polyamines, whereby there are enabled toners with many of the advantages illustrated herein including excellent high image fixing characteristics, the absence or minimization of toner agglomeration, the absence or minimization of image ghosting, and retention or substantial retention of the core components, avoiding or minimizing toner agglomeration. In another embodiment, the present invention relates to a pressure fixable encapsulated toner composition wherein the shell is comprised of the reaction product of a mixture of a glycidyl-functionalized reagent or reagents, a polyisocyanate or polyisocyanates selected, for example, from the group consisting of benzene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, polymethylene diisocyanate, and other aliphatic and aromatic polyisocyanates with a polyamine. The aforementioned toners possess a number of advantages as illustrated herein, including preventing or minimizing leaching or loss of the core components, espeically the core resin. In another embodiment of the present invention, the toner compositions obtained include thereon an electroconductive material thereby rendering the compositions relatively conductive with a controlled and stable volume resistivity such as, for example, from about 10.sup.3 to about 10.sup.8 ohm-cm, and preferably from about 5.times.10.sup.4 and 5.times.10.sup.7 ohm-cm, which toners are particularly useful for inductive single component development processes.
Examples of advantages associated with the toner compositions of the present invention in embodiments thereof are as indicated herein, and include excellent image fix and image crease, rub and abrasion resistance, the elimination and/or the minimization of image ghosting, excellent fixing characteristics, acceptable surface release properties, substantially no toner agglomeration, acceptable powder flow characteristics, and minimal or no leaching of the core components. Also, the toners of the present invention in embodiments thereof possess a shell with substantially improved mechanical properties thus permitting, for example, improved toner shelf stability; and moreover, the shell precursors selected possess in many instances low vapor pressures, thus reducing environment hazards, which is not the situation with some of the prior art toner shells. Further, with the toner compositions of the present invention, in various embodiments the shell does not rupture prematurely causing the core component comprised, for example, of a polymer resin and magnetite, or other pigment to become exposed, which upon contact with other toner particles or reprographic development subsystem component surfaces and the like can form undesirable agglomerates. The excellent surface release properties possessed by the toners of the present invention provide for a complete or substantially complete transfer of toned images to a paper substrate during the development process, thus rendering this process very efficient. Furthermore, the toner compositions of the present invention can be obtained in high reaction yields in several embodiments thereof, and the preparative process can involve a simple washing and sieving procedure to remove the undesirable coarse and fine particles without utilizing the costly conventional particle size classification step. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. In an embodiment, the toner compositions of the present invention are selected for pressure fixing processes, for ionographic printing wherein dielectric receivers, such as silicon carbide, are utilized, reference U.S. Pat. No. 4,885,220, the disclosure of which is totally incorporated herein by reference. In one embodiment, the toner compositions of the present invention can be selected for image development in commercial Delphax printers such as the Delphax S9000.TM., S6000.TM., S4500.TM., S3000.TM., and Xerox Corporation printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized, that is fixing of the developed image is accomplished by simultaneously transferring and fixing the developed images onto a paper substrate with pressure. Another application of the toner compositions of the present invention is for two component development systems wherein, for example, the image toning and transfer are accomplished electrostatically, and the fixing of the transferred image is achieved by application of pressure with or without the assistance of thermal energy.
The toner compositions of the present invention can, in one embodiment, be prepared by interfacial polymerization involving microcapsule shell-forming polycondensation, followed by an in situ core resin forming, free radical polymerization of a core monomer or monomers in the presence of a free radical initiator. Thus, in one embodiment the present invention is directed to a process for a simple and economical preparation of pressure fixable encapsulated toner compositions by interfacial/free-radical polymerization methods wherein there are selected core monomers, pigments, a free radical initiator, and certain shell precursors capable of providing, after interfacial polycondensation, a polar condensation polymer shell which contains polar functional groups such as urea, urethane, glycidyl and hydroxy functions. Other process embodiments of the present invention relate to, for example, interfacial/free radical polymerization methods for obtaining encapsulated colored toner compositions. Further, in another process aspect of the present invention the encapsulated toners can be prepared in the absence of solvents thus eliminating explosion hazards associated therewith and the expensive and hazardous solvent separation and recovery steps. Moreover, with the process of the present invention in an embodiment there are obtained improved toner throughput yields per unit volume of reactor size. The toners of the present invention are useful for permitting the development of images in reprographic imaging systems, inclusive of electrostatographic and ionographic imaging processes wherein pressure fixing is selected, and for other imaging and printing processes.
The toner compositions of the present invention contain unique shell materials that permit the containment or substantial retention of the core components, thus eliminating or substantially suppressing core resin diffusion and leaching in embodiments. As a consequence, the problems of toner agglomeration and image ghosting can be completely or substantially eliminated. Furthermore, the toner compositions of the present invention dramatically improve the efficiency of the image transfer process to substrates such as paper in many embodiments. Also, with the toner compositions of the present invention, particularly with respect to their selection for single component inductive development processes, the toner particles can contain on their surfaces a uniform and substantially permanently attached electroconductive materials thereby imparting stable electroconductive characteristics to the particles inclusive of situations wherein these particles are subjected to vigorous agitation. With many of the prior art toners, the surface conductivity properties of the toner particles may be unstable when subjected to agitation, especially for example, when electroconductive dry surface additives such as carbon black are selected. Further, with the aforementioned prior art toner compositions, there are in many instances obtained images of low quality with substantial background deposits, particularly after a number of imaging cycles, especially subsequent to vigorous mechanical agitation which results in toner electroconductivity instability since the additives, such as carbon black, are not permanently retained on the surface of the toner. Additionally, several of the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions are obtained by processes which utilize organic solvents as diluting or reaction media. The utilization of organic solvents renders the preparative process costly and potentially hazardous since most organic solvents are flammable and explosion-prone, and such processes also require expensive solvent separation and recovery steps. Moreover, the inclusion of solvents also decreases the toner throughput yield per unit volume of reactor size. Furthermore, with many of the prior art processes toners of narrow size dispersity cannot be easily achieved as contrasted with the process of the present invention where narrow particle size distributions are generally obtained in embodiments thereof. In addition, many prior art processes provide deleterious effects on toner particle morphology and bulk density as a result of the removal of solvent and the subsequent collapse or shrinkage of toner particles during the toner work-up and isolation processes resulting in a toner of very low bulk density. These disadvantages are substantially eliminated with the toners and processes of the present invention. More specifically, thus with the encapsulated toners of the present invention control of the toner physical properties of both the core and shell materials can be achieved in embodiments thereof. Specifically, with the encapsulated toners of the present invention undesirable leaching or loss of core components is avoided or minimized, and image ghosting is eliminated in many instances primarily in view of the presence of the polar functional groups within the shell polymer, and thus the low permeability characteristics of the shell structure to the core components. Image ghosting is an undesirable phenomenon encountered in ionographic transfix development when, for example, certain toner compositions are utilized. It refers to the repetitious printing of unwanted images, and arises primarily from the contamination of the dielectric receiver by the unremovable residual toner materials. This problem can sometimes be partially eliminated by the use of suitable surface release agents which aids in the removal of residual toner materials after image transfer. The toner compositions of the present invention eliminate or substantially eliminate the image ghosting problem by providing a microcapsule shell which effectively contains the core resin, inhibiting its leaching, and prevents it from coming into contact with the dielectric receiver during the image toning and transfix processes. In addition, the shell materials of the present invention in embodiments thereof also provides excellent surface release properties, thus enabling efficient removal of residual toner materials from the dielectric receiver surface. Furthermore, the excellent surface release properties afforded by the shell can dramatically enhance the image transfer efficiency of the transfix development processes.
A poly(aminohydrin-urethane) shell of the present invention in an embodiment thereof is obtained by the copolymerization of a bis(epoxy)-functionalized monomer with a diamine in the presence of a diisocyanate. The amino content of the shell can vary, however, those with an aminohydrin content of less than 30 mole percent and from about 1 to about 25 mole percent can exhibit excellent resistance to toner agglomeration in embodiments of the present invention.
Encapsulated cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of known advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since the toner compositions selected can be fixed without application of heat. Nevertheless, some of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fixed under high pressure, which generally shortens the useful life of the imaging components such as the dielectric receiver or pressure roll. High pressure fixing can also result in unacceptable paper calendering. Also, a number of the prior art cold pressure fixable toner compositions, particularly those prepared by conventional melt blending processes, do not usually provide high image fix levels. As a result, these images can be of low fix levels, and of low crease, rub and smear resistant. Additionally, some of the cold pressure fixing toner compositions of the prior art have other disadvantages in that, for example, these compositions when fixed under high pressure provide, in some instances, images of low resolution and high image gloss.
In a patentability search report, the following United States patents were listed; U.S. Pat. No. 4,833,057 which discloses a toner comprising as a main component a urethane-modified polyester obtained by reacting a polyester resin with an isocyanate compound, see for example the Abstract of the Disclosure; U.S. Pat. No. 4,575,478 which discloses a toner comprising an epoxy resin, or modified epoxy resin obtained by the reaction of an epoxy resin with a polyfunctional compound having at least two carboxyl or amino groups per molecule, and a bivalent or polyvalent metal complex compound, see the Abstract of the Disclosure for example; neither of the aforementioned patents, according to the search report, disclose an encapsulated toner; and U.S. Pat. Nos. 4,455,362; 4,464,281; 4,520,091 and 4,877,706, which relate to encapsulated toners with shells obtained from diisocyanates and from diepoxy/diamine copolymers.
The following U.S. patents are mentioned: U.S. Pat. No. 3,967,962 which discloses a toner composition comprising a finely divided mixture comprising a colorant material and a polymeric material which is a block or graft copolymer, including apparently copolymers of polyurethane and a polyether (column 6), reference for example the Abstract of the Disclosure, and also note the disclosure in columns 2 and 3, 6 and 7particularly lines 13 and 35; however, it does not appear that encapsulated toners are disclosed in this patent; U.S. Pat. No. 4,565,764 which discloses a microcapsule toner with a colored core material coated successively with a first resin wall and a second resin wall, reference for example the Abstract of the Disclosure and also note columns 2 to 7, and particularly column 7, beginning at line 31, wherein the first wall may comprise polyvinyl alcohol resins known in the art including polyurethanes, polyureas, and the like; U.S. Pat. No. 4,626,490 contains a similar teaching as the '764 patent, and more specifically discloses an encapsulated toner comprising a binder of a mixture of a long chain organic compound and an ester of a higher alcohol and a higher carboxylic acid encapsulated within a thin shell, reference the Abstract of the Disclosure, for example, and note specifically examples of shell materials in column 8, beginning at line 64, and continuing on to column 9, line 17, which shells can be comprised, for example, of polyurethanes, polyurea, epoxy resin, polyether resins such as polyphenylene oxide or thioether resin, or mixtures thereof; and U.S. patents of background interest include U.S. Pat. Nos. 4,442,194; 4,465,755; 4,520,091; 4,590,142; 4,610,945; 4,642,281; 4,740,443 and 4,803,144.
There are disclosed in U.S. Pat. No. 4,307,169, the disclosure of which is totally incorporated herein by reference, microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes can be selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions usually containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Interfacial polymerization processes are described in British Patent Publication 1,371,179, the disclosure of which is totally incorporated herein by reference, which publication illustrates a method of microencapsulation based on in situ interfacial condensation polymerization. More specifically, this publication discloses a process which permits the encapsulation of organic pesticides by the hydrolysis of polymethylene polyphenyl isocyanate, or toluene diisocyanate monomers. Also, the shell-forming reaction disclosed in the aforementioned publication is initiated by heating the mixture to an elevated temperature at which point the isocyanate monomers are hydrolyzed at the interface to form amines, which then react with unhydrolyzed isocyanate monomers to enable the formation of a polyurea microcapsule wall. Moreover, there is disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, interfacial polymerization processes for pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctadecylvinylether-co-maleic anhydride as a soft component.
Other prior art, primarily of background interest, includes U.S. Pat. Nos. 4,254,201; 4,465,755 and Japanese Patent Publication 58-100857. The Japanese publication discloses a capsule toner with high mechanical strength, which is comprised of a core material including a display recording material, a binder, and an outer shell, which outer shell is preferably comprised of a polyurea resin. In the '201 patent, there are disclosed encapsulated electrostatographic toners wherein the shell material comprises at least one resin selected from polyurethane resins, a polyurea resin, or a polyamide resin. In addition, the '755 patent discloses a pressure fixable toner comprising encapsulated particles containing a curing agent, and wherein the shell is comprised of a polyurethane, a polyurea, or a polythiourethane. Moreover, in the '201 patent there are illustrated pressure sensitive adhesive toners comprised of clustered encapsulated porous particles, which toners are prepared by spray drying an aqueous dispersion of the granules containing an encapsulated material.
Also, there are illustrated in U.S. Pat. No. 4,280,833 encapsulated materials prepared by interfacial polymerization in aqueous herbicidal compositions. More specifically, as indicated in column 4, beginning at line 9, there is disclosed a process for encapsulating the water immiscible material within the shell of the polyurea, a water immiscible organic phase which consists of a water immiscible material, that is the material to be encapsulated, and polymethyl polyphenyl isocyanate is added to the aqueous phase with agitation to form a dispersion of small droplets of the water immiscible phase within the aqueous phase; and thereafter, a polyfunctional amine is added with continuous agitation to the organic aqueous dispersion, reference column 4, lines 15 to 27. Also of interest is the disclosure in column 5, line 50, wherein the amine selected can be diethylene triamine, and the core material can be any liquid, oil, meltable solid or solvent soluble material, reference column 4, line 30. A similar teaching is present in U.S. Pat. No. 4,417,916.
In U.S. Pat. No. 4,599,271, the disclosure of which is totally incorporated herein by reference, there are illustrated microcapsules obtained by mixing organic materials in water emulsions at reaction parameters that permit the emulsified organic droplets of each emulsion to collide with one another, reference the disclosure in column 4, lines 5 to 35. Examples of polymeric shells are illustrated, for example, in column 5, beginning at line 40, and include isocyanate compounds such as toluene diisocyanate and polymethylene polyphenyl isocyanates. Further, in column 6, at line 54, it is indicated that the microcapsules disclosed are not limited to use on carbonless copying systems; rather, the film material could comprise other components including xerographic toners, see column 6, line 54.
In U.S. Pat. No. 4,520,091, the disclosure of which is totally incorporated herein by reference, there is illustrated an encapsulated toner material wherein the shell can be formed by reacting a compound having an isocyanate with a polyamine, reference column 4, lines 30 to 61, and column 5, line 19; and U.S. Pat. No. 3,900,669 illustrating a pressure sensitive recording sheet comprising a microcapsule with polyurea walls, and wherein polymethylene polyphenyl isocyanate can be reacted with a polyamide to produce the shell, see column 4, line 34.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending U.S. application Ser. No. 718,676 (now abandoned), the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process. Further in copending U.S. application Ser. No. 402,306, the disclosure of which is totally incorporated herein by reference, there are illustrated encapsulated toners with a core comprised of a polymer binder, pigment or dye; and thereover a polymeric shell, which contains a soft and flexible component, permitting, for example, proper packing of shell materials resulting in the formation of a high density shell structure, which can effectively contain the core binder and prevent its loss through diffusion and leaching process. The soft and flexible component in one embodiment is comprised of a polyether segment. Specifically, in one embodiment there is disclosed in the aforementioned copending application encapsulated toners comprised of a core containing a polymer binder, pigment or dye particles, and thereover a shell preferably obtained by interfacial polymerization, which shell has incorporated therein a polyether structural moiety. Another embodiment of the copending application is directed to encapsulated toners comprised of a core of resin binder, pigment dye or mixtures thereof, and a polymeric shell of a polyether incorporated polymer, such as a poly(ether urea), a poly(ether amide), a poly(ether ester), a poly(ether urethane), mixtures thereof, and the like. The aforementioned toners can be prepared by an interfacial/free radical polymerization process involving dispersing a mixture of core monomers, colorants, free-radical initiator, and one or more water-immiscible shell precursors into microdroplets in an aqueous medium containing a stabilizer. One of the shell precursors in this organic phase is a polyether-containing monomers or prepolymers. The nature and concentration of the stabilizer employed in the generation of stabilized microdroplets depend mainly, for example, on the toner components, the viscosity of the mixture, as well as on the desired toner particle size. The shell forming interfacial polymerization can be effected by addition of a water soluble shell monomer into the reaction medium. The water soluble shell monomer in the aqueous phase reacts with the water immiscible shell precursors in the organic phase at the microdroplet/water interface resulting in the formation of a microcapsule shell around the microdroplet. The formation of core binder from the core monomers within the newly formed microcapsule is subsequently initiated by heating, thus completing the formation of an encapsulated toner. In embodiments thereof (1) the compositions of the present invention utilize a very polar shell polymer wherein polar functional groups, such as hydroxy functions, are all present in the shell polymer structure; (2) the toner compositions of the present invention employ a polar shell which inhibits core resin leaching or diffusion primarily because of its incompatibility with the relatively nonpolar core resin; and (3) the toner compositions of the present invention also provide images of high abrasion resistance, presumably because of the strong interactions of the polar shell material with paper.
Accordingly, there is a need for encapsulated toner compositions with many, and in some embodiments substantially all the advantages illustrated herein. More specifically, there is a need for encapsulated toners with shells that eliminate or minimize the loss of core components such as the core resin. Also, there is a need for encapsulated toners wherein images with excellent resolution and superior fix are obtained. Moreover, there is a need for encapsulated toners, including colored toners wherein image ghosting and toner offsetting and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with, in some instances, excellent surface release characteristics to enhance toner transfer efficiency in the transfix ionographic imaging systems. Furthermore, there is a need for encapsulated toners, including colored toners, which exhibit no toner agglomeration thus providing a long toner shelf life exceeding in embodiments, for example, one to two years. Also, there is a need for encapsulated toners that have been surface treated with additives, such as carbon blacks, graphite or the like, to render them conductive to a volume resistivity level of preferably from about 1.times.10.sup.3 to 1.times.10.sup.8 ohm-cm, and to enable their use in single component inductive development systems. Further, there is a need for encapsulated toners wherein surface additives, such as metal salts or metal salts of fatty acids and the like, are utilized to primarily assist in toner surface release properties. There is also a need for processes for the preparation of encapsulated toners with the advantages described hereinbefore. There is also a need for interfacial polymerization microencapsulation processes for black and colored encapsulated toner compositions, wherein the core contains a colorant or colorants, and a core resin derived from in situ free radical polymerization of an addition-type monomer or monomers, which core is encapsulated in a polar condensation polymeric shell. Furthermore, there is a need for toners and improved processes thereof that will enable the preparation of pressure fixable encapsulated toner compositions whose properties such as shell strength, nature of core resin, the core resin molecular weight and molecular weight distribution can be desirably controlled. Moreover, there is a need for toner compositions which provide high image fix levels as well as excellent abrasion and crease resistance characteristics.